This invention relates to a calibration standard, especially for the calibration of devices for the non-destructive measurement of the thickness of thin layers with a carrier layer of a basic material and a standard applied on the carrier layer, said standard having the thickness of the layer to be measured at which the device is to be calibrated.
For the non-destructive measurement of the thickness of thin layers by a magnetic induction method or an eddy current method depending on the basic material, it is necessary that—after a standardization—the devices are calibrated to the corresponding measuring task. By means of the calibration, a difference between nominal and actual values is established. This difference will be corrected, with the device being calibrated to the measuring task.
For the correction of the difference between nominal and actual value, a measurement by means of the calibration standard is performed. To start with, a first value is registered on a carrier layer consisting of a basic material. Following that, another value is registered on a standard which is applied on the carrier layer. The difference will be the measured layer thickness. Due to the standard, the nominal value to be measured is determined. After several measurements, the averaged deviation between nominal and actual values will be registered and calibrated.
The calibration standards known so far consist of a carrier layer of the basic material on which the standard is applied or glued on as a plastic film such as, for example, polyethylene terephthalate (PTFP). The calibration standards are used for the reproduction of layer thicknesses from e.g. 40 μm to 1,000 μm. With these calibration standards, it is problematic—in particular in the lower range of the layer thickness—that the application or especially the gluing can already result in minor build-ups by the bonding agent, with the reproduced layer thickness being distorted. The use of such films has the additional disadvantage that they are ductile and have a rough surface.